Question 30: NCERT Solutions for 12th Class Physics: Chapter 11-Dual Nature of Radiation and Matter
Light of intensity 10-5 W m-2 falls on a sodium photo-cell of surface area 2 cm2. Assuming that the top 5 layers of sodium absorb the incident energy, estimate time required for photoelectric emission in the wave-picture of radiation. The work function for the metal is given to be about 2 eV. What is the implication of your answer?
Wave picture of radiation state that incident energy is uniformly distributed among all the electrons continuously. Let us first calculate the total number of recipient electrons in-5 layers of sodium. Consider each sodium atom has one electron free as conduction electron. Effective atomic area = 10-20 m2 Number of conduction electrons in 5 layers
Where experimental observation shows that emission of photo electrons is instantaneous = 10-9 sec Thus wave picture fails to explain photoelectric effect.
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NCERT Solutions for 12th Class Physics: Chapter 11-Dual Nature of Radiation and Matter